This article originally appeared in Scarabogram, Sept. 1994,
New Series No. 173, pp. 2-3.

Metriona bicolor
adult; length 5.5-6 mm

Few who see the "gold bug" forget it. It is one of the most striking insects
in the Puget Sound area. The golden tortoise beetle is a stunning, vibrant metallic
gold color. It has a magical quality, not only because of the brilliance of
its color, but also because the brilliance isn't permanent. Metriona
can alter color within a short time period, turning from brilliant gold to a
dull, spotty reddish color. The gold color also fades when the insect dies.
What controls the color while the insect is alive is an intriguing question,
but one for which I have no answer. [The gold color is caused by a thin layer
of moisture between the cuticle and an inner layer of the elytra. Apparently
the insect is able to "voluntarily" squeeze this layer, reducing its thickness
and eliminating the gold color. This change also occurs involuntarily when the
beetle is under moisture stress, and, of course, when it dies. ---editor.]

A bit smaller than the more familiar ladybird beetles, the golden tortoise
beetle is configured somewhat like a safari hat with a narrow "shelf" skirting
the outside of the wing covers and thorax. This "shelf" causes the resemblance
to a tortoise, hence the name. Tortoise beetles are plant eaters, like most
Chrysomelids [leaf beetles]. The golden tortoise beetle in particular feeds
on morning glory. They reside under the leaf, eating a series of small holes
resulting in a characteristic damage pattern (see figure below).

Metriona damage on
morning glory

The larval stage of Metriona is at least as interesting as the adult,
though perhaps not as magical. The larvae also feed on the underside of morning
glory leaves. When they shed their skin, it remains attached to a prong-like
process at the end of the abdomen. Molts are stacked on molts, and are carried
around held over the insect's back like a parasol. "Parasol beetles" is indeed
another common name for tortoise beetles. When disturbed, the larvae wave the
parasol about, no doubt to intimidate or distract potential predators.

Tortoise beetles overwinter as adults. In the spring the adults begin to
feed, mate, and lay eggs. The larvae emerge and feed through the summer, and
pupate in late summer. Adults reportedly emerge in the early fall, feeding until
the morning glory gives up the ghost for the current season, and then hunker
down among plant debris for the winter. I've only seen tortoise beetles on morning
glory, which, in my opinion, is poetic justice. I wonder, however, if in the
spring they might use alternate food plants since it takes a while for morning
glory to put out many leaves, concentrating as they do on getting those stems
out there. Natural history observations would be welcome, fellow Scarabs. Remember
as you pass vacant lots to look for morning glory and holes in leaves. And do
take a minute to look underneath.

Hatch, Melville H. 1971. The Beetles of the Pacific Northwest. Volume 5, p.
238. University of Washington Publications in Biology, vol. 16, University of
Washington Press.

Mason, 1929. Entomological News, vol. 40: 52-56.

Riley, E.G. 1986. Review of the tortoise beetle genera of the tribe Cassidini
occurring in America north of Mexico. Journal of the New York Entomological
Society, 94(1): 98-114. [changes scientific name of species from M.bicolor
to Charidotella bicolor. This change does not seem to be widely accepted.
It is in 6 scientific papers (3 by Riley himself) but Metriona is still
used in 53 out of 70 nontechnical sources.]